A vehicle is equipped with components which are driven by engine. For example, the engine is equipped with an alternator, a compressor for air conditioner, a high-pressure pump for increasing fuel pressure, an oil pump, a motor generator, and the like. Since, these components are driven by the engine, a fluctuation in engine speed and/or unintentional acceleration/deceleration of the vehicle may be arose when driving torque of the components are rapidly changed.
Japanese Patent No. 2709061 shows that an intake air amount and an ignition timing are corrected at a time of switching of an air-conditioner in order to restrict the fluctuation in idle speed due to the switching of air-conditioner.
Generally, since the engine torque is controlled based on a throttle position (intake air amount) or a fuel injection amount, a response delay exists in an intake system. That is, there is time lag between a time when the throttle position is varied and a time when the engine torque is changed.
In the above Japanese Patent, both intake amount and ignition timing are corrected when the air-conditioner is turned on/off. The correction of the engine torque based on the correction of the ignition timing causes no response delay unlike the correction of the intake air amount. The torque correction amount which is delayed by the intake air amount correction is ensured by the correction of the ignition timing.
However, the torque which can be ensured by correcting the ignition timing is limited. When the ignition timing is close to a knocking limit or a stable combustion limit, a permitted correcting range of the ignition timing is relatively narrow and the torque correction amount is small. Thereby, when the driving torque of components are rapidly changed, even if both intake air amount and ignition timing are corrected, the torque correction amount runs shortage relative to the rapid change in driving torque of the components, which may cause the fluctuation in engine speed and the acceleration/deceleration of the vehicle.
The above fluctuation in engine speed and the acceleration/deceleration of the vehicle can be restricted if the increased (decreased) driving torque of the components are canceled by the increased (decreased) engine torque. In this case, the increased/decreased amount of driving torque of components may be estimated based on control parameters of the components. However, the estimated value of the increased/decreased amount of driving torque of the components must includes some errors due to a individual productive dispersion or an aging thereof. Furthermore, the engine torque command value may be deviated from the actual engine torque due to such a dispersion and aging.
Even if the increased amount (decreased amount) of the driving torque of the components and the increased amount (decreased amount) of the engine torque are controlled in synchronization with each other, the torque error cannot be avoided. The above fluctuation in engine speed and unintentional acceleration/deceleration cannot be restricted enough.